The Power of Numbers A Single Statistic Can Strengthen Public Support for Traffic Safety Laws

Knowing the risk increased support of laws aimed at drunk driving and red-light running, among others

Public support for effective road safety laws, already solid, can be strengthened by a single number: a statistic that quantifies the traffic-related injury risks associated with a given law, according to a new study from the Johns Hopkins Center for Injury Research and Policy at the Johns Hopkins Bloomberg School of Public Health.

The study, published in the September issue of Accident Analysis &Prevention, surveyed 2,397 adults nationwide about their attitudes toward four types of road-safety laws —mandatory ignition interlock installation for people convicted of driving under the influence (DUI), the use of red-light cameras in school zones, a requirement that in-vehicle information entertainment systems be disabled when a car is moving and the mandatory use of bicycle helmets for children under 16. After indicating their initial support or opposition for each law, respondents were given a statistic about the injury risk addressed by each law or the efficacy of the laws in reducing that risk. Afterward, respondents were asked again about their attitudes toward the laws.

The majority of survey respondents were initially either supportive or strongly supportive of each of the four laws. Nearly three out of four (74.8 percent) participants were in favor of the requirement that children under 16 wear bicycle helmets, and nearly as many (74.4 percent) supported mandatory ignition interlock installation for DUI offenders. More than three out of five (61.4 percent) were initially in favor of a requirement that in-vehicle infotainment systems lock when a car is moving, and close to as many (58 percent) supported the use of red-light cameras in school zones.

For each of the four laws, support increased significantly after participants were given a statistic about related injury risks or how each law would reduce those risks. Nearly a third (30.7 percent) of respondents became more supportive of the law pertaining to in-vehicle infotainment systems; close to one in four (22.2 percent) increased their support for the red-light camera law, and one in five (20 percent) became more supportive of both the bicycle helmet and ignition interlock laws.

“We are very encouraged by the results of this study, the benefits of which have potential for broad application,” says Katherine Clegg Smith, PhD, lead author of the study and faculty member at the Johns Hopkins Center for Injury Research and Policy. “In our analysis, research-informed evidence considerably increased public support for safety initiatives that are known to make a difference. Knowing that scientific evidence influences public opinion provides support for continuing to generate and share research on injury prevention policies to better inform the public about key safety issues.”